Imidazolidine and 1,4-diazepane analogs of N-(2-benzofuranyl)methyl-N'-(4-alkoxybenzyl)piperazines were prepared to explore the effect of ring contraction and expansion on σ receptor affinity and subtype selectivity within a series of cyclic diamines. In vitro receptor binding assays revealed that all cyclic vicinal diamines possessed affinity and selectivity for σ(1) receptors. The imidazolidines possessed nanomolar σ(1) affinities (K(i)=6.45-53.5 nM), and relatively low levels of subtype selectivity (σ(2)/σ(1)=58-237). However, the piperazines and diazepanes achieved picomolar σ(1) interactions, with K(i) ranges of 0.05-10.28 and 0.10-0.194 nM, respectively. Moreover, the piperazines and diazepanes showed excellent discrimination over the σ(2) receptor, with σ(1) selectivities of 143-16140 and 220-11542, respectively.
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